Tanks, sewers, and other enclosures that must be entered periodically require some type of air ventilation system for the men working in the enclosure. Without some type of air ventilation the workers would be required to wear respirators. The current apparatus used today normally includes an air pump outside the enclosure and an 8-inch flexible hose leading into the enclosure. However, the normal 24 inch (or smaller) manhole is barely large enough to allow a worker to enter the enclosure with tools and/or materials. When an 8-inch ventilating hose is also located within the manhole, it may prevent the worker from entering the enclosure, and it always provides an obstruction that tends to catch tools on the worker's belt, with the possibility of damaging the hose or dropping tools on another worker already in the enclosure.
This invention relates to a method and apparatus for passing air into an enclosure through a manhole with a minimum of obstruction at the manhole. In one exemplary embodiment, the conduit comprises a central section having a cross section in the shape of a crescent or a segment of a circle, two intermediate sections attached respectively to each end of the central section, and each having a cross-sectional shape varying from the shape of the central section at the juncture with said central section, and tapering to a circular shape at the outer end of the associated intermediate section. The conduit also includes two outer cylindrical sections, respectively attached to the outer end of each of the intermediate sections, the outer sections being externally aligned on a common axis.
As a result of this construction, it is possible to reduce the cross-sectional obstruction of a relatively small manhole, i.e., with about a 20 inch diameter, to about 10 percent of the cross-sectional area of the manhole, as compared to about 35 percent obstruction for a standard 8 inch diameter hose. For larger manholes, the percent obstruction using the conduit of this invention may be substantially less than 10 percent.
In this exemplary embodiment of the invention, an outer surface of the central section is cylindrical and has substantially the same diameter as the diameter of the manhole in which the conduit is used. In the interest of economy, however, it is practical to utilize a standard size conduit which will fit virtually all conventional manholes. For example, a central section having a radius of curvature conforming to a smaller manhole radius, may be effectively utilized in all larger manholes as well.
It is also a feature of this invention that the cross-sectional area of the central section may be reduced in comparison to the outer cylindrical sections, but only to the extent of causing a reduction of not more than about 10 percent in air flow rate, as explained below.
It is also a feature of this invention that means are provided at the outer surface of the central section of the conduit so that the conduit may be hung or otherwise attached at the manhole opening.
A related process in accordance with the invention, in its broadest aspects, includes the steps of providing a ventilation conduit as described above, locating the conduit so that one outer end and an associated intermediate section lie outside the enclosure, the other outer end and its associated intermediate section lie inside the enclosure, and the central section extends through the manhole; and operatively connecting the conduit to an external source of air, such as a pump.
It is therefore an object of this invention to provide an improved air conduit and related process for ventilating an enclosure with a manhole entrance. It is another object of this invention to provide such an air conduit which is somewhat "flattened" in the area where it passes through the manhole so as to obstruct not more than about ten percent of the cross-sectional area of the manhole, without any significant reduction in air flow through all sections of the conduit. Still other objects will appear in the more detailed description which follows.